1. Field of the Invention
The present invention relates to media for tape recording systems and Hard Disk Drives (HDDs). More particularly, the present invention relates to a technique for improving media recording performance of tape recording systems and HDDs.
2. Description of the Related Art
Magnetic recording disks are currently made having a continuous magnetic layer that is deposited on a suitable aluminum alloy or glass ceramic substrate. The materials, or media, used for the magnetic layer are generally nickel, cobalt or iron alloys that have been deposited by evaporation or by sputtering to form a magnetic recording layer. Data is written to the magnetic layer by applying a localized magnetic field using a recording head that flies over the surface of the magnetic layer. In perpendicular recording, the media is magnetized perpendicularly to the plane of the disk and each magnetic bit consists of several hundred small grains having a predominant magnetization direction. In longitudinal recording, the magnetization is oriented in the plane of the disk. More recently, other orientations of the magnetization have been proposed to take advantage of the minimum in the Stoner-Wohlfarth switching astroid for different magnetic recording media.
Each grain of a magnetic recording medium ideally has a single magnetization axis such that the magnetization can lie in one of two directions separated by 180 degrees. The magnetization transition between adjacent bits follows a line between the grains of the respective bits. In a perfect medium, the grains on either side of a transition would have opposite magnetization directions. Such a condition would occur only when the grains are subjected to weak magnetic coupling. When the magnetic coupling between two adjacent bits is too great, though, the transition between adjacent bits is poorly defined. Further, the magnetization vectors of each grain within a bit should align in a single direction, which is a state that is more easily obtained when the grains have strong magnetic coupling and is in contrast to the requirement for a weak magnetic coupling for a well-defined transition between adjacent bits. Additionally, thermal fluctuations cause grain magnetization to spontaneously reverse when the volume of the effective magnetic unit is less than a certain minimum, causing loss of data. As the volume of the effective magnetic unit increases, the coupling between grains increases and thereby enhances stability.
It follows that, in view of the conflicting requirements relating to the exchange coupling between adjacent bits and within a given bit and the effects of thermal fluctuations, the degree of coupling between grains is a key parameter that critically affects the performance of a magnetic recording medium. In that regard, the need for controlling exchange coupling between grains is well known. See, for example, U.S. Pat. No. 5,834,085 to Lairson et al.
Recent studies of perpendicular recording media have suggested that the presence of some exchange coupling between grains can lead to an enhancement of the recording performance and thermal stability. Coupled granular/continuous (CGC) media have been proposed as one technique for controlling exchange coupling in a continuous medium. A typical CGC medium consists of a Pt-rich CoCrPt layer having poor Co grain segregation and a thin Pt layer improves the reversal nucleation field of a Co70Cr18Pt12 medium from +420 to −600 Oe. The thermal decay of the signal amplitude from recorded transitions is reduced from 2.23% to 0.10% per decade. Unity squareness has been obtained for a thin Pt capping layer with a magnetization decay rate of 0.21% per decade. See, for example, Y. Sonobe et al., “Thermally Stable CGC Perpendicular Recording Media with Pt-Rich CoPtCr and Thin Pt layers,” IEEE Transactions On Magnetics, Vol. 38, No. 5, pp. 2006-2011, September 2002. CGC media having a Co/Pd multilayer capping structure has also been shown to improve thermal stability without compromising SNR. See, for example, Y. Sonobe et al., “Thermal Stability and SNR of Coupled Granular/Continuous Media,” IEEE Transactions On Magnetics, Vol. 37, No. 4, pp. 1667-1670, July 2001. Extra layers, however, are required, thereby increasing the medium and deposition tool complexity.
Ion beam treatments have been described for the purpose of improving tribological performance. See, for example, U.S. Pat. No. 6,368,425 to Segar et al. Additionally, ion beam treatments have also been described as a technique for patterning recording media. See, for example, U.S. Pat. No. 6,383,597 to Fullerton et al. Ion beam treatments have also been described in JP 1110757A to K. Akiysau as a technique for producing isolated magnetic grains by a process that forms defects and “micronizes” (or pulverizes) existing grains. Such a known process requires only 1010 ions/cm2 for H, He, Li, or Be, as compared to >1013 ions/cm2 for the technique of the present invention.
What is required is a technique for optimizing the exchange coupling of a perpendicular magnetic recording medium that is independent from the deposition process of the magnetic medium.